FOXBORO FBM205 P0914XG I/O Interface Module

Key features of the FBM205 are:

• Four redundant 20 mA dc analog input channels
• Four redundant 20 mA dc analog output channels
• Each input and output channel is galvanically isolated
• Compact, rugged design suitable for enclosure in Class G3 (harsh) environments
• Execution of an analog input application program that provides conversion time and configurable options for Rate of Change Limits
• Configurable options in the modules for output security include Fail-Safe Action
• High accuracy achieved by sigma-delta data conversions for each channel
• Termination Assemblies (TAs) for locally or remotely connecting field wiring to the FBM205
• Redundant loop power on FBM powered transmitters
• 3-tier termination assembly for per channel internally and/or externally loop powered transmitters.

The FBM205, 0 to 20 mA I/O Interface (Redundant) contains four redundant 0 to 20 mA dc analog input channels and four redundant 0 to 20 mA dc analog output channels. The inputs/outputs are galvanically isolated from other channels and ground.

A redundant pair of the modules combine to provide redundancy at the Fieldbus Module (FBM) level, with field I/O wired to one common termination assembly (see Figure 1). Each module independently attempts to hold the output(s) at its specified output value(s), and each independently reports its observed value of the inputs.

A redundant analog input and redundant analog output block in the control software validates each input and output in conjunction with information to/from the module.

A redundant analog output function block, AOUTR, is used for each redundant pair of outputs. The AOUTR block handles output writes and initialization logic for the redundant channels. On each execution cycle of the AOUTR block, identical output writes are sent to both modules, fully exercising the fieldbus and the logic circuitry of each module. When a failure is detected in one of the modules, its output is driven to 0 mA and the corresponding channel in the good module automatically continues supplying the proper current to the output current loop.

A redundant analog input function block, AINR, is used for each redundant pair of inputs. The AINR block handles input reads and initialization logic for the redundant channels. On each execution cycle of the AINR block, identical reads are sent to both modules, fully exercising the fieldbus and the logic circuitry of each module.

Each input channel accepts an analog sensor input such as a 4 to 20 mA transmitter or a self-powered 4 to 20 mA source. Each output channel drives an external load and produces a 0 to 20 mA output. Transmitter power from each module is diode OR'd together in the redundant adapter to ensure redundant power. The microprocessor of each module executes the analog I/O application program, plus security routines that validate the health of the FBM.

Input channel options include a configurable choice of integration time on a per module basis. Input channel security is enhanced by redundantly powering the input current loop from per channel power supplies in each module of the pair.

Configurable options in the modules for output security include Fail-Safe Action (Hold/Fallback), Analog Output Fail-Safe Fallback Data (on a per channel basis), Fieldbus Fail-Safe Enable, and Fieldbus Fail-Safe Delay Time. The Analog Output Fail-Safe Fallback Data option must be set for 0 mA output. This removes one of the pair of redundant output channels from service for detectable problems such as a module not properly receiving output writes or not passing security tests on FBM microprocessor writes to output registers. Setting of the Analog Output Fail-Safe Fallback Data option for 0 mA output also minimizes the possibility of a "fail high" result.